1. Field of the Invention
This invention relates to a method for removing dielectric and/or magnetic foreign matters from objects being processed, utilizing static electricity and/or magnetic force.
2. Prior Art
There is known, for example, a method in which dielectric foreign matters such as a small insect and a hair mixed in foodstuffs are removed therefrom utilizing static electricity to keep the foodstuffs sanitary. In this conventional method, a high voltage is applied to an electrode portion of a static electricity generating device so as to attract to a surface of the electrode portion dielectric foreign matters which have bee introduced into objects being processed (foodstuffs). Then, the foreign matters thus stuck to the electrode surface are blown off by a blast of air and are drawn into a duct, thereby removing the dielectric foreign matters.
Another method is known to remove foreign matters of a magnetic nature, such as particles of iron, which have been introduced into objects being processed (e.g., a foodstuff, plastic product or electronic component) during various treatments. In this known method, the removal of such magnetic foreign matters is effected utilizing a magnetic force. More specifically, a magnetic pole portion of an electromagnet or a permanent magnet is disposed close to a conveyer line along which the objects are being transferred, so that the magnetic pole portion can attract such magnetic foreign matters mixed in the objects. Then, in the case of the electromagnet, the thus attracted foreign matters are separated from the magnetic pole portion for collection by inverting the polarity of the electromagnet at suitable frequency. In the case of the permanent magnet, such attracted foreign matters are removed from the permanent magnet by mechanically scratching them off the magnetic pole portion.
With the former method, however, upon lapse of several seconds after the sticking of the dielectric foreign matters by electrostatic induction to the electrode portion having a polarity opposite to that of the charges of the attracted dielectric foreign matters, electric charges of the same polarity as the electrode portion is accumulated on the attracted dielectric foreign matters. As a result, the foreign matters tend to separate from the electrode portion to drop on the objects being processed.
A problem with the latter method is that part of the fine magnetic foreign matters tend to remain on the surface of the magnetic pole portion, which periodically requires such operation that the transfer of the objects and manufacturing processes are stopped in order to clean the magnetic pole portion. This is undesirable from the viewpoint of productivity.